Barn swallows before barns: population histories and intercontinental colonization

Area of Science:

• Evolutionary Biology
• Ornithology
• Population Genetics

Background:

• The barn swallow (Hirundo rustica) is a globally distributed species.
• Its wide range is partly attributed to adapting to human-made structures for nesting.
• Understanding its recent evolutionary history is key to explaining its distribution patterns.

Purpose of the Study:

• To investigate the recent evolutionary history and phylogenetic relationships of the barn swallow.
• To explore the genetic basis for its adaptation to human structures and wide distribution.
• To identify ancestral origins and dispersal patterns of Hirundo rustica.

Main Methods:

• Phylogenetic analysis using mitochondrial (mtDNA) and nuclear DNA.
• Sequencing of a sex-linked nuclear gene to assess recent evolutionary events.
• Molecular divergence calibration to estimate dispersal timing.

Main Results:

• Strongly supported mitochondrial DNA clades identified for Europe, Asia, and North America plus the Baikal region.
• Nuclear gene analysis did not recover mtDNA splits, indicating recent divergence.
• North American barn swallows recently colonized the Baikal region, an unexpected dispersal direction.
• Palearctic clades show recent gene flow, linked to expansion via human settlements.
• North American populations appear historically larger and more stable than Palearctic ones.

Conclusions:

• The barn swallow's ancestral area is likely the Holarctic region, with vicariance driving divergence.
• Recent colonization of the Baikal region by North American barn swallows occurred earlier than anticipated.
• Human-provided nesting sites have facilitated range and population expansion in Palearctic barn swallows.
• Barn swallow populations in North America exhibit greater historical stability compared to Palearctic populations.